This section provides background information related to the present disclosure which is not necessarily prior art. This section also provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
The present invention concerns a material that displays piezoelectric and ferroelectric properties. Piezoelectricity refers to the accumulation of an electric charge due to the application of mechanical stress. These materials also exhibit the reverse effect: when subject to an electrical charge, they will undergo mechanical strain.
Ferroelectric materials contain a permanent dipole which allows them to maintain a polar electric field when they are not subjected to an external field. All ferroelectric materials display piezoelectricity. There is interest in using polymers to create such materials due to the fact that polymers are lightweight, low cost, and relatively easy to process as compared to intermetallic compounds. Piezoelectric polymers, such as poly (vinylidene fluoride) (PVDF) and its copolymers, have the potential to achieve large strains and high working energy density under external electrical fields, which is very promising for biomimetic actuators and artificial muscle technologies.
Poly (vinylidene fluoride) (PVDF) is a polymer that shows promise as a ferroelectric materials. In addition to an amorphous phase, PVDF can crystallize into multiple phases with different chain conformations known as α, β, and γ-phase. Only the β-phase has strong ferroelectric and piezoelectric properties because of its planar conformation and high dipole density.
Previous methods to produce ferroelectric PVDF rely on combinations of annealing, controlled solvent evaporation, and uni-axial stretching of a sample. These methods yield a final product that lacks thermal stability or contains an insufficient proportion of the β-phase.
The ferroelectric β-phase has only been obtained through use of a drawing process (typically 300-400% elongation). Thus only thin films can be effectively produced, placing limits on the potential application space and transducer design.